Direct Evidence of Interfacial Freeze-to-Activation Transition Regulating the Reversal of Time–Temperature-Dependent Macroscopic Dynamics in Polymer Nanocomposites

The macroscopic dynamics of polymer nanocomposites is largely governed by the dynamic characteristics of the constrained polymer layer at the filler surface. Particularly in rubber nanocomposites, the dynamics of the interfacial layer directly determines the service performance, yet its quantitative link to macroscopic viscoelasticity remains unclear. This work employs nanorheology and reveals that the constrained interfacial layers undergo a transition from freeze to activated state at a specific frequency/temperature (1 kHz/∼10 °C). With increasing filler content, this transition reverses the temperature/frequency dependence of the macroscopic dynamics of the nanocomposites. Before and after interfacial activation, the dominant mechanism of macroscopic viscoelasticity undergoes a fundamental shift, with the interfacial overlap effect playing a key role in this shift. Prior to the activation of the interface, interfacial overlap and freeze enhance with increasing filler content; the bulk dissipation is dominated by the matrix and decreases as filler content increases. Once the interface is activated, the bulk dissipation becomes dominated by the interface, where overlap imposes a higher energy barrier for segmental relaxation, leading to an enhancement in bulk dissipation with increasing filler content. By precisely measuring nanoscale dynamics of the constrained interface and refining the classical Zorowski-Murayama model, we achieved high-precision prediction of bulk viscoelasticity in the composites. The improved model achieves a prediction accuracy exceeding 97% at 25 Hz. This work elucidates the intrinsic correlation between interfacial constrained segmental dynamics and macroscopic viscoelasticity, providing a general theoretical and methodological framework for dynamics regulation in multiphase nanocomposites and the design of high-performance viscoelastic materials.